High-pressure discharge lamp

ABSTRACT

High-pressure discharge lamp, with an outer bulb ( 10 ), on which a first terminal ( 12 ) and a second terminal ( 14 ) are provided, and with a discharge vessel ( 16 ), which is accommodated in the outer bulb ( 10 ), with a first and a second terminal ( 18, 20 ) and with an ignition apparatus ( 22 ), which is accommodated in the outer bulb ( 10 ) and is connected between the first terminal ( 12 ) of the outer bulb and the first terminal ( 18 ) of the discharge vessel ( 16 ). A switch ( 32 ), which closes depending on temperature, is connected in parallel with the ignition apparatus ( 22 ) between the first terminal ( 12 ) of the outer bulb ( 10 ) and the first terminal ( 18 ) of the discharge vessel ( 16 ). During operation of the lamp, the current therefore flows past the spiral pulse generator ( 32 ), so that no power is lost.

TECHNICAL FIELD

The invention relates to a high-pressure discharge lamp as claimed inthe preamble of patent claim 1. It also relates to a method for drivinga high-pressure discharge lamp as claimed in the preamble of patentclaim 5.

PRIOR ART

Such a high-pressure discharge lamp and such a method are described inDE 10 2005 061 832 published after the filing date of the presentapplication. FIG. 1 shows, schematically, the most important componentsof such a high-pressure discharge lamp. A lamp outer bulb, which isgiven the overall designation 10, is illustrated symbolically by meansof a dash-dotted contour. On the outer bulb there is a first connection12 and a second connection 14. The second connection 14 is connected toground, for example. At the heart of the lamp there is a dischargevessel 16 with a first connection 18 and a second connection 20 in thelamp outer bulb 10, said second connection 20 likewise being connectedto ground. A spiral pulse generator 22 is interposed between the firstconnection 12 of the lamp outer bulb 10 and the first connection 18 ofthe discharge vessel. “Interposed” is in this case understood to meanthat a possible current flows via a first line path 24 of the spiralpulse generator, while the second line path 26 is not connected to thedischarge vessel. The first line path 24 and the second line path 26 canbe bridged with the aid of a short-circuiting switch 28. The second linepath 26 is connected to ground via a charging resistor 30.

The spiral pulse generator 22 is used for igniting the active gaslocated in the discharge vessel 16. After the ignition, a currentpredetermined by the external circuitry of the lamp flows through thedischarge vessel 16 and therefore from the first connection 12 of thelamp outer bulb 10 to the second connection 14, i.e. in particular viathe interposed voltage generator 22 or, more precisely, via the firstline path 24 of the spiral pulse generator 22. As a result of theinternal resistance of the spiral pulse generator 22, there is thereforea voltage drop across the spiral pulse generator 22. Thus, electricalpower is converted into heat in the spiral pulse generator 22 duringnormal lamp operation, in addition to the heat generated by thedischarge vessel. This power is lost for the lamp, with the result thatthe system efficiency is correspondingly reduced. The generator isadditionally heated, with the result that its life is shortened.

DESCRIPTION OF THE INVENTION

The object of the invention is to overcome the mentioned disadvantageswhich the high-pressure discharge lamp as claimed in the preamble ofpatent claim 1 has as described with reference to FIG. 1 and inparticular to provide a high-pressure discharge lamp with good ignitionperformance, in which some of the power is not lost as a result of theinterposition of a spiral pulse generator. The object is achieved by ahigh-pressure discharge lamp having the features as claimed in patentclaim 1 and a method having the features as claimed in patent claim 5.

According to the invention, a switch which closes as a function oftemperature is connected in parallel with the ignition apparatus betweenthe first connection of the outer bulb and the first connection of thedischarge vessel. Since the discharge vessel 16 is heated to aconsiderable extent during operation—shortly after ignition a value of500° C., for example, is reached at the base of the discharge vessel—theswitch is therefore closed during operation and the ignition apparatusis bridged. The disadvantage that a voltage drop occurs across theignition apparatus and thus power is lost is thus eliminated. Theinvention is not dependent on the ignition apparatus used; a spiralpulse generator is preferably used.

The temperature-dependent switch is preferably a bimetallic switch. Abimetallic, switch has the advantage that it also opens again as afunction of temperature. Thus, a further disadvantage of the prior artresulting from the fact that a heated discharge vessel requires a higherignition voltage is also overcome. Often, after prolonged operation, thedischarge vessel is heated to such an extent that if it is switched offand switched on again after a short period of time it cannot immediatelyreignite. A corresponding ignition apparatus then only applies voltageswhich are too low. When using the bimetallic switch, the ignitionapparatus remains bridged, even if the lamp is switched off, until thedischarge vessel has cooled down to a sufficient extent. The ignitionapparatus is therefore not activated in vain in the case of the lampbeing switched on again, but remains inactive.

A suitable closing temperature, i.e. the temperature at which the switchcloses once the temperature has increased, is between 70° C. and 500°C., preferably between 90° C. and 350° C. The lower limit is primarilydetermined on the basis of typical temperatures which can prevail in thecase of given environmental influences in the lamp outer bulb; it shouldbe at least 10° to 15° above these temperatures. A possible upper valuefor the closing temperature results from the proximity of, the switch,which closes as a function of temperature, to the discharge vessel andthe desired switchover speed, to be precise both as far as closing andreopening is concerned.

The method according to the invention for driving a high-pressuredischarge lamp in which ignition takes place by means of an ignitionapparatus, which is arranged, together with a discharge vessel, in anouter bulb of the high-pressure discharge lamp is characterized in that,after the ignition, a switch is activated which guides the currentrequired for operation of the high-pressure discharge lamp past theignition apparatus. The switch is preferably activated thermally. Themethod can be further developed by the use of the high-pressuredischarge lamp in the embodiments previously mentioned.

BRIEF DESCRIPTION OF THE DRAWING

A preferred embodiment of the invention will be described below withreference to the drawing, in which:

FIG. 1 shows, schematically, the essential components of a high-pressuredischarge lamp of the (subsequently published) prior art, on which theinvention is based, and

FIG. 2 shows, schematically, the essential components of a high-pressuredischarge lamp according to the invention.

PREFERRED EMBODIMENT OF THE INVENTION

FIG. 2 shows the essential components, arranged in a lamp outer bulb 10,of a high-pressure discharge lamp according to the invention in anillustration similar to that in FIG. 1, with the same reference numeralsbeing used for the same components.

The initial position was that a spiral pulse generator 22 was interposedbetween the input 12 of the lamp outer bulb 10 and the input 18 of thedischarge vessel 16. The invention now provides a bimetallic switch 32,which closes in the event of an increase in the temperature and isconnected in parallel with the spiral pulse generator 22 (more preciselyto the first line path 24 thereof), i.e. is likewise interposed betweenthe connection 12 of the lamp outer bulb 10 and the connection 18.

The spiral pulse generator is still used for igniting the lamp, i.e. theactive gas located in the discharge vessel 16. This is described moreprecisely in DE 10 2005 061 832, with a subsequent publication date. Theclosing bimetallic switch 32 is active after the ignition if, owing tothe operation of the lamp, the temperature in the lamp outer bulb 10increases. If the closing temperature of the bimetallic stwitch 32 isreached, said bimetallic switch closes and prevents the operatingcurrent flowing via the discharge vessel (from the connection 12 to theconnection 14 of the lamp outer bulb 10) from causing a considerablevoltage drop, which brings about a power loss. The spiral pulsegenerator 22 provided merely for the ignition is therefore bypassed inthe circuitry once its function has been performed. The high pressuredischarge lamp from DE 10 2005 061 832, which has improved ignitioncapacity, is thereby further optimized.

1. A high-pressure discharge lamp with an outer bulb (10), on which afirst connection (12) and a second connection (14) are provided, andwith a discharge vessel (16) accommodated in the outer bulb (10) with afirst and a second connection (18, 20) and with an ignition apparatus(22), which is accommodated in the outer bulb (10) and is connectedbetween the first connection (12) of the outer bulb and the firstconnection (18) of the discharge vessel (16), characterized in that aswitch (32) which closes as a function of temperature is connected inparallel with the ignition apparatus (22) between the first connection(12) of the outer bulb (10) and the first connection (18) of thedischarge vessel (16).
 2. The high-pressure discharge lamp as claimed inclaim 1, the ignition apparatus being a spiral pulse generator (22). 3.The high-pressure discharge lamp as claimed in claim 1 or 2,characterized in that the switch which closes as a function oftemperature is a bimetallic switch (32).
 4. The high-pressure dischargelamp as claimed claim 1 or 2, characterized in that the switch (32)closes in the event of an increase in temperature to a closingtemperature, which is between 70° C. and 500° C., preferably between 90°C. and 350° C.
 5. A method for driving a high-pressure discharge lamp,in which ignition takes place by means of an ignition apparatus (22),which is arranged, together with a discharge vessel (16), in an outerbulb (10) of the high-pressure discharge lamp, characterized in that,after the ignition, a switch (32) is activated which guides the currentrequired for operation of the high-pressure discharge lamp past theignition apparatus (22).
 6. The method as claimed in claim 5,characterized in